Night vision system for motor vehicles

ABSTRACT

An infrared lighting device for motor vehicles, for example a headlight, has a radiation source and a filter, whereby the device emits white and infrared radiation at a certain intensity in a wavelength range between 800 and 1200 nm on one axis, and the filter at a first angle may transmit a first visible part and at a second angle different from the first may transmit a second visible part of the radiation source, and both parts transmitted form white light.

This invention concerns night vision auxiliary systems for motorvehicles. Systems are known that comprise an infrared headlight, whichbeams radiation to the outside in front of the vehicle, as well as aninfrared camera and a system for transmitting an image taken by thecamera in visible form to the driver. The headlight has a source ofwhite light and a filter, which suppresses the visible part of theradiation from the radiation source and transmits the part that is inthe infrared range.

However, in practice, this type of filter often lets through some of thevisible radiation, especially the radiation in the red color range. Butin a headlight, any such red colored radiation that gets through, nomatter how intense, is disturbing, since it can cause another driver tobecome confused between the front lighting and the back lighting of thevehicle. Improving the filter in terms of suppressing the red lightwhile keeping the useful part of the infrared radiation, i.e., theradiation in the range between 800 nm and 1000 nm, is expensive. Theproblem is that the range to be suppressed (red) is directly connectedto the useful infrared range that gets through. For this, thecharacteristic transmission curve of the filter would have to have steepedges since the very good suppression necessary in the red range isopposed to the very good transmission necessary in the IR range.

To solve this problem, DE 699 03 076 discloses an infrared lightingdevice that includes a filter whose transmission ratio is designed insuch a way that it emits white and infrared radiation along one axis ofthe device, whereby the intensity of the white radiation can becompletely different from zero, but amounts to less than 2000 Cd.

This is done by having the filter transmit infrared beams (IR beams),ultraviolet beams (UV beams) and visible near-blue and near-red beamsand visible primary beams with a yellow-green primary color betweenthem. FIG. 1 shows schematically the transmission ratio T of a filter,as it can be used as a function of the wavelength ë according to oneembodiment in DE 699 03 076. The residual visible radiation it transmitsis then added to a white color effect.

Such filters can be produced by a multilayer system. Their reflectionand characteristic transmission curves are essentially based oninterference effects. In the state of the art, the filter is made so itmay transmit the visible radiation from a radiation source in such a waythat there is a synthesis of the visible transmitted part of the whitelight (see Claim 3 of DE 699 03 076). Since interference filters exhibitangle-dependent transmission behavior, the filter must be adjusted tothe respective lighting geometry of the headlight. For example, FIG. 3 ashows a headlight 2 with lighting geometry in which the filter 10 isbasically acted on vertically. On the other hand, the lighting geometryof the headlight in FIG. 3 b results in an impact geometry in which thevertical impact plays basically no role. But adjusting the filter to arespective new geometry is time-consuming and hence expensive.

The problem to be solved with this invention is therefore to provide afilter whose characteristic transmission curve has great tolerance tovariations in lighting geometry.

Another problem to be solved is the design fluctuations involved inproducing such interference filters which are difficult to avoid. Thebasic parameters for the characteristic transmission curve include theoptical layer thickness and the indices of refraction of the layers.Slight fluctuations in these parameters during the coating process or,what is much more probable, from one coating to the next, can have animpact on which parts of the visible light will be transmitted. It isdifficult to make sure that only a small part of the visible radiationgets through (for example in the range of 0.5%), and small uncertaintiesin transmission can cause large changes in the color effect.

Another problem to be solved with this invention is therefore to providean interference filter needed for high-yield lighting devices that canbe produced without requiring cost-intensive measures to reduceproduction fluctuations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically the transmission ratio T of a filter, as itcan be used as a function of the wavelength e.

FIG. 2 shows schematically how blue, green, red, and yellow coloreffects are assigned to a corresponding diagram.

FIG. 3 a shows a view of the impact geometry of the night-visionauxiliary headlight with a vertical filter.

FIG. 3 b shows a view of the impact geometry of the night-visionauxiliary headlight with a slanted filter.

FIG. 4 shows a magnified view of the range in FIG. 2.

FIG. 5 shows a corresponding spectral range of the filter in thenight-vision auxiliary system.

FIG. 6 a shows a schematic layout of a night-vision auxiliary headlight.

FIG. 6 b shows the results of optimization in an angle shift of thefilter.

THE SOLUTION ACCORDING TO THE PRESENT INVENTION

As a person skilled in the art knows, color effect is determined bybasically 3 factors: a) the characteristic radiating curve of the lightsource (typical light sources reach their maximum in the green oryellow-green spectral range), b) a physiological factor, which isconnected with the wavelength-dependent light sensitivity of the humanvision system, whereby light sensitivity is highest in yellow and c) thecharacteristic transmission curve of the optical system used.Technically, the color effect can be specified by means of so-calledcolor coordinates. FIG. 2 shows schematically how blue (B), green (G),red (R) and yellow (Y) color effects are assigned to a correspondingdiagram. FIG. 2 also shows the range, surrounded by a broken line, inwhich a white color effect prevails.

The cross-hatched area in FIG. 2 gives the legal range for this type ofsystem according to the so-called ECE Standard, which must be met here.This permitted range is shown again magnified in FIG. 4.

The radiation coming from a lighting device must be within this ECErange to match legal requirements. The problem now is to do this fordifferent impact geometries at the same time. As a rule, the typicalradiation sources beam in the directions in which they actually radiate,with basically the same characteristic spectral curve. To achieve thedesired tolerance in terms of impact geometry, the filter according tothe present invention has the property, for a wide range of angles ofincidence, of transmitting part of the visible radiation and doing it sothat white light is transmitted for basically each of the angles ofincidence in the range itself.

This can be brought about by having the radiation transmitted go to thesame color coordinates after it comes out of the filter for basicallyeach angle in the range. Such a restrictive condition is not evennecessary, however. As the inventor found, one need only make sure thatfor the range of angles of incidence, the color coordinates are withinthe legal range. As the inventor also found, it is very advantageous toallow a variation along the blue-yellow axis (FIG. 4 along axis A-A′).When interference filters are produced, during both the design phase andthe production phase, special care must be taken that the characteristictransmission curve of the filter is especially stable in the greenrange. This is both in terms of production tolerances and in terms ofangle dependence. This makes fewer demands on stability in the blue andyellow-red ranges. As a result, there are variations in the colorcoordinates in terms of the angle of incidence and/or the productiontolerances. These variations basically come into play, however, alongaxis A-A′ in FIG. 4. This makes it easier and better to comply with thelegal requirements than was possible in the state of the art in thepast.

An example will now be used to describe in detail the production of thefilter in the invention for a range of angles from 0° to 40°, whichproduces color coordinates that are all within the ECE white range.

The filter should be used in a night-vision auxiliary system outfittedwith an Osram H11 type (12 V, 55 W, 64211 SUP) halogen headlight lamp.The corresponding spectral range is shown in FIG. 5. The schematiclayout of such a headlight is shown in FIG. 6 a.

A Corning Glass substrate is used as the substrate material for thefilter.

In the example, the coating materials used are niobium oxide as thehigh-refractive and SiO2 as the low-refractive material for the filter.Possible alternative coating materials would be, for example, titaniumoxide/silicon oxide or tantalum oxide/silicon oxide.

To find the thickness needed for the multilayer system, a commercialthin-layer computer program was used (OptiLayer for Windows by Messrs.A. Tikhonravov and M. Trubetskov).

By means of a so-called RayTrace Program (ASAP, commercial software),i.e., with software that allows optical paths of beams in complexoptical systems to be simulated, the relevant angles of incidence arefound. For the example to be described here, the calculation with ASAPshows that the “center of gravity” angle of incidence on the filter is20°. However, to be largely independent of the precise system layout,the design is also optimized for 0 to 40°, so that the variations runalong the “ECE white-range axis” (FIG. 4 along axis A-A′).

For this, the design is optimized in steps for one angle after theother. First, a design is found that transmits for 20° angles ofincidence in the visible range in the center less than 0.5%. The designshould also have a steep edge, whose T=50% point in the example is at780 nm and that transmits more than 75% for the infrared range(wavelengths 800-1000 nm). In addition, in order to protect the humaneye while the headlight is in use, the design is made so that as ofapprox. 1040 nm on a width of at least 25 nm in the near infrared range,less than 60% are transmitted.

After that, for the 20° angle of incidence the color coordinates need tobe optimized in such a way that it is as central as possible in therange of the ECE standard (hence as close as possible to and preferablyprecisely the coordinates: x=0.375 and y=0.375). However, the specialcharacteristics of the filter need to remain the same (low transmissionin the visible, high transmission in teh infrared) during theoptimization. Then, the color coordinates are optimized for the anglesof incidence 0°, 30° and 40°, so that they fall within the range of theECE standard. However, for these angles of incidence, the colorcoordinates produced are not necessarily the same as for the 20° angleof incidence. All that is required is that the angle shift run as muchas possible within the ECE white range along the axis shown in FIG. 4 byreferences A-A′. This is very easy to do if care is taken that thespectra of the different angles for the green range (480-580 nm) havethe smallest possible change. The result of such optimization is shownin FIG. 6 b for angles of incidence of 0°, 10°, 20, 30° and 40°. TheA-A′ axis can be defined by means of the straight line equationy=0.695*x+0.1. FIG. 6 b shows that as the angle of incidence rises, thex coordinate rises monotonic. Preferably the y coordinate should, withan x coordinate that lies in the interval 0.31≦x≦0.45, deviate by amaximum of 0.025 from the straight line defined. For smaller x, thecolor site is no longer in the ECE range, for larger x, a ratherhorizontal course is desirable, since here the ECE range has thecorresponding course.

Change is limited in the green range by having this range heavilyweighted in the optimization. This is necessary not only to guaranteethat the filter design for the angles of incidence from 0° to 40° runalong the ECE white range, but also to keep the change in lightintensity small, since the green range has the greatest impact on this.

Table 1 shows the breakdown of the optical layer thickness design andthe refractive index used.

The refractive index of the materials used is 2.34 for niobium oxide and1.47 for silicon oxide.

Sputter technology was used in the example to produce the filter (morespecifically: reactive DC magnetron sputtering). In situ, during theprocess, the optical spectra are registered continuously (monitoring),and the sputter process is corrected if deviations from the desiredspectrum calculated are measured. This ensures that the filters madeactually have the required optical characteristic curves, especially inthe green range. In other words: so that the color coordinates arewithin ECE white, production monitoring of the product is weightedhighest especially in the wavelength range from 480-580 nm.

Other coating techniques can also be used as alternatives. Among themare in general PVD and CVD processes. As the PVD processes, for example,thermal evaporation can be used. Preferably thermal evaporation issupported by ion bombardment (ion assisted deposition, IAD).

If such a filter is built into the optical path of a light beam, aninfrared lighting device for motor vehicles, for example a headlight,can be made with at least one source of radiation and a filter, wherebythe device may emit on one axis of the device a white and infraredradiation in a wavelength range that is between 800 and 1200 nm, wherebythe infrared radiation has an intensity of more than 25 W/sr, and thewhite radiation has an intensity not equal to zero of less than 2000 Cd.The filter may transmit a first visible part of a first partial beamfrom the radiation source at a first angle and a second visible part ofa second partial beam from the radiation source at a second angledifferent from the first. The first angle is basically different fromthe second angle. In this context “basically” means at least 0.5°. It ischaracteristic that the first visible part transmitted is white light,and the second visible part transmitted is white light.

Layer (counted Optical Layer from substrate) Thickness [nm] Material 1108 SiO2 2 73 Nb2O5 3 127 SiO2 4 144 Nb2O5 5 133 SiO2 6 100 Nb2O5 7 109SiO2 8 94 Nb2O5 9 97 SiO2 10 101 Nb2O5 11 111 SiO2 12 90 Nb2O5 13 110SiO2 14 110 Nb2O5 15 104 SiO2 16 83 Nb2O5 17 120 SiO2 18 132 Nb2O5 19119 SiO2 20 142 Nb2O5 21 147 SiO2 22 122 Nb2O5 23 120 SiO2 24 117 Nb2O525 171 SiO2 26 127 Nb2O5 27 134 SiO2 28 149 Nb2O5 29 158 SiO2 30 126Nb2O5 31 118 SiO2 32 142 Nb2O5 33 154 SiO2 34 152 Nb2O5 35 144 SiO2 36173 Nb2O5 37 154 SiO2 38 204 Nb2O5 39 156 Nb2O5 40 173 SiO2 41 156 Nb2O542 148 SiO2 43 243 Nb2O5 44 168 SiO2 45 136 Nb2O5 46 193 SiO2 47 139Nb2O5 48 213 SiO2 49 146 Nb2O5 50 207 SiO2 51 145 Nb2O5 52 98 SiO2

1. An infrared lighting device for motor vehicles with at least oneradiation source that emits white light and a filter, whereby the devicemay emit white and infrared radiation on one axis in a wavelength rangebetween 800 and 1200 nm, whereby the infrared radiation has an intensityof more than 25 W/sr and the white radiation an intensity less than 2000Cd, however not equal to zero, and the filter at a first angle maytransmit a first visible part of white light from a first partial beamfrom the radiation source, and the filter at a second angle differentfrom the first may transmit a second visible part of white light from asecond partial beam from the radiation source, characterized by the factthat the second angle is different from the first and the first visiblepart transmitted is white light and the second visible part transmittedis white light.
 2. The infrared lighting device in claim 1,characterized by the fact that the larger of the two angles leads to anx coordinate of the color site of the corresponding visible parttransmitted that is larger than the x coordinate of the color site ofthe visible part transmitted at the smaller angle.
 3. An infraredlighting device for motor vehicles with at least one radiation sourcethat emits white light and a filter, whereby the device on one axis mayemit white and infrared radiation in a wavelength range between 800 and1200 nm, whereby the infrared radiation has an intensity of more than 25W/sr, and the white radiation has an intensity not equal to zero of lessthan 2000 Cd, characterized by the fact that for any pair of angleswithin the range from 0° to 40°, with the first angle and a second angledefined, the filter at the first angle may transmit a first visible partof a first partial beam from the radiation source, and the filter at thesecond angle, different from the first, may transmit a second visiblepart of a second partial beam from the radiation source, wherein thefirst visible part transmitted forms white light, and the second visiblepart transmitted forms white light.
 4. The infrared lighting device inone of claims 2 or 3, characterized by the fact that the respective ycoordinates of the color site of the visible part transmittedcorresponding to the angles deviates no more than 0.025 from that of thestraight line defined by the equation y=0.695*x+0.1, for x coordinatesin the interval 0.31≦x≦0.45.
 5. A lighting device for a headlightprovided to a motor vehicle comprising: a radiation source that emits afirst partial beam and a second partial beam; a filter positionedadjacent to the radiation source to filter the first partial beamforming a first angle of incidence relative to the filter and the secondpartial beam forming a second angle of incidence relative to the filter,wherein the first and second angles of incidence are different, and thefilter transmits a first visible portion of the first partial beam and asecond visible portion of the second partial beam, the transmittedportions including a color effect corresponding to an x color coordinateof less than or equal to about 0.5 on a spectrum of colors visible tohumans, and further wherein the lighting device emits at least white andinfrared radiation along an axis in a wavelength range between 800 and1200 nm, wherein the infrared radiation has an intensity of more than 25W/sr and the white radiation an intensity of less than 2000 Cd, but notequal to zero.
 6. The infrared lighting device according to claim 5,wherein both the first and second visible parts transmitted lead to acolor site on a visible color spectrum having a y coordinate that isless than or equal to about 0.275 on the visible color spectrum.
 7. Thelighting device according to claim 5, wherein a larger of the first andsecond angles of incidence results in a transmitted portion that has acolor effect characterized by an x color coordinate that is larger thanan x color coordinate of the transmitted portion of the first and secondbeam forming a smaller angle of incidence relative to the filter.
 8. Thelighting device according to claim 5, wherein the angle of incidence ofat least one of the first and second beams is about 20°, and the x colorcoordinate of the transmitted portion is about 0.375.
 9. The lightingdevice according to claim 8, wherein the transmitted portion includes ay color coordinate of about 0.375.
 10. The lighting device according toclaim 5, wherein respective y color coordinates of the color effectexhibited by the visible portions transmitted deviate no more than 0.025from a straight line defined by the equation y=0.695*x+0.1, wherein xrepresents x color coordinates in an interval of 0.31≦x≦0.45.
 11. Aninfrared lighting device for motor vehicles with at least one radiationsource and a filter, whereby the device may emit white and infraredradiation on one axis in a wavelength range between 800 and 1200 nm,whereby the infrared radiation has an intensity of more than 25 W/sr andthe white radiation an intensity less than 2000 Cd, however not equal tozero, and the filter at a first angle may transmit a first visible partof a first partial beam from the radiation source, and the filter at asecond angle different from the first may transmit a second visible partof a second partial beam from the radiation source, wherein the secondangle is different from the first and the first visible part transmittedis white light and the second visible part transmitted is white light,and the larger of the two angles leads to an x coordinate of the colorsite of the corresponding visible part transmitted that is larger thanthe x coordinate of the color site of the visible part transmitted atthe smaller angle.
 12. The infrared lighting device according to claim11, wherein both the x color coordinate corresponding to the firstvisible part and the x color coordinate corresponding to the secondvisible part are less than or equal to about 0.5.
 13. The infraredlighting device according to claim 12, wherein both a y color coordinatecorresponding to the first visible part and a y color coordinatecorresponding to the second visible part are greater than or equal toabout 0.375.
 14. The infrared lighting device according to claim 11,wherein respective y color coordinates corresponding to the first andsecond visible parts transmitted by the filter deviate no more than0.025 from a straight line defined by the equation y=0.695*x+0.1,wherein x represents the x color coordinates in an interval of0.31≦x≦0.45.
 15. An infrared lighting device for motor vehicles with atleast one radiation source and a filter, whereby the device on one axismay emit white and infrared radiation in a wavelength range between 800and 1200 nm, whereby the infrared radiation has an intensity of morethan 25 W/sr, and the white radiation has an intensity not equal to zeroof less than 2000 Cd, characterized by the fact that for any pair ofangles within the range from 0° to 40°,with the first angle and a secondangle defined, the filter at the first angle may transmit a firstvisible part of a first partial beam from the radiation source, and thefilter at the second angle, different from the first, may transmit asecond visible part of a second partial beam from the radiation source,wherein the first visible part transmitted forms white light, the secondvisible part transmitted forms white light, and the respective ycoordinates of the color site of the visible part transmittedcorresponding to the angles deviates no more than 0.025 from that of thestraight line defined by the equation y=0.695*x+0.1, for x coordinatesin the interval 0.31≦x≦0.45.